Some years ago a COG member took the time to analyze the Connie tank and found that the lower "cheeks" by where your knees go hold about 1/3 gallon of water, rust, mud, dirt, dead insects, sub-microscopic alien spaceships, and miscellaneous other crud, that cannot be drained out except by dismounting the tank and running it all out the filler hole and the petcock mounting hole, and flushing with new fuel. This area is below the level of the fuel petcock, so there's no other way to get it out. You really really need to do this about once a year.